Communication devices operating in Time Division Multiplexing (TDM) systems are required to alternate between transmit and receive at high rates. Switching frequencies as high as 1 KHz are common in such applications which requires that the transmitters be on for a period of 1 ms and off for a period of 1 ms. The short on cycle of these transmitters puts stringent requirements on their amplifiers that have to reach full power in a fraction of the transmitter on time. Furthermore, in portable radios operating from battery power, there is a great need for power amplifiers which exhibit high operating efficiencies and low current drain characteristics. This is due to the limited amount of battery capacity available in portable radios, combined with the increasing demands by radio users to operate radios for longer periods of time without recharging the batteries. Since the power amplifiers sued in radios are one of the key current consuming devices of a radio, there is always a need for higher efficiency amplifiers in radio designs.
Unfortunately, high efficiency amplifiers which exhibit fast turn on cycles such as "class B" amplifiers, tend to have problems with what is known as frequency splatter, due to the fact that a Class B amplifier will turn on very quickly (as soon as an input signal to the amplifier is applied which is high enough to bias the amplifier). Tis high speed turn on and off operation of the amplifier causes frequency splatter to be transmitted which is undesired. Frequency splatter not only causes interference with the transmitted signal on nearby channels, but also causes problems in meeting regulator agency requirements (e.g. FCC, etc.) that most countries impose on communication equipments.
An amplifier circuit which can attain high efficiencies, as well as exhibit minimal frequency splatter would be very useful for use in communication equipments, and would be especially useful in TDM applications.